She appeared with her husband Arwel Wyn Jones – who just happens to be Sherlock's production designer – at this week's Sherlock Holmes Convention in Vienna and revealed some precious secrets from the BBC1 drama. The Q&A is reported in full on somelikeitpink's tumblr but here are the highlights.

1. When Benedict Cumberbatch first did the pilot, his hair was dyed dark to resemble the famous Sherlock
Holmes. What the make-up team didn't foresee were his bleached locks
(he'd just played Van Gogh), which turned a lovely shade of green the
day before filming began. Cue a last minute dash to the
hairdressers....

2. Jim the IT guy had tinted eyelashes (according to Sherlock) but Jim Moriarty went one better. In addition to the slicked hair and pale pallor of Sherlock's
arch-nemesis, the production team reached into their make-up bags to
help Andrew Scott perfect Moriarty's "cold stare". What did they use?
Guy-liner.

3. The moustache. A point of contention, apparently, when Martin Freeman
had to sport the facial accessory for the start of series three.
According to Pritchard-Jones, they had to try over ten different
versions before Martin finally agreed to one. He also shaved it off
sooner than originally planned in the script.

4. Rupert Graves flirts with Una Stubbs. (And she loves it!)

5. The licking scene between Charles Augustus
Magnussen (played by Lars Mikkelsen) and Lady Smallwood (Lindsay Duncan)
in His Last Vow resulted in a few queasy stomachs amongst the crew but
the make-up team were on hand with tons of mouth wash, mints and some
face wipes for poor Lindsay. Apparently a few of the takes were much
worse than the one they ended up using.

6. Claire gets to hang out with Benedict Cumberbatch
every morning. Sometimes he'll come in and have loads of lines to learn
but then there are the days they turn the music up and have a party. A
PARTY.

"That was a really interesting one," Scott told Digital Spy
of the hallucinatory scene. "It was part of an extraordinary sequence
that I thought was really beautifully directed, and read fantastically
well on the page.

"It was a case of removing myself a little bit
from Moriarty, because it was in Sherlock's mind palace. So it allowed
me to go to real extremes with the character, to see what he would be
like were he completely unleashed.

"I like being able to see
Moriarty through Sherlock's eyes, it's such an interesting angle on the
character. It's an insight into the mind of the hero, as much as
anything, so it was good to be able to play a different note."

Scott
went on to discuss the show's acknowledgement of its passionate online
fan base, which notably inspired a fantasy sequence in which Sherlock
and Moriarty kiss.

Sherlock confronts Moriarty in 'The Reichenbach Fall'

"I like the fact that, in a playful way, the third series included
[the fans]," Scott mused. "For the most part, they're very enthusiastic
and respectful people, and the support has just been extraordinary."

Scott also confirmed that he knows the truth behind series three's climactic twist, in which Moriarty appears to announce his return from the grave via a video message broadcast across every screen in the UK.

"I do know the answer to that question, yes, and I'm not going to tell you!"